The present invention relates to an optical fiber cable using a multicore fiber, and is preferred to the case where crosstalk is suppressed.
Optical fibers for use in generally widely available optical fiber communication systems have a structure in which the outer circumference of a single core is surrounded by a cladding, and optical signals are propagated through the inside of this core to transmit information. Information volumes to be transmitted are dramatically increased in association with the widespread use of optical fiber communication systems. In association with an increase in information volumes to be transmitted as described above, in the optical fiber communication system, long distance optical communications of a large capacity are conducted using a large number of optical fibers. Moreover, such an optical fiber cable is used in which these optical fibers are provided in a sheath to form a cable.
On the other hand, in order to decrease the number of optical fibers in the optical fiber communication system, it is known that a multicore fiber is used in which the outer circumferences of a plurality of cores are surrounded by a single cladding, and a plurality of signals is transmitted on light propagated through the cores.
Patent Literature 1 below describes an optical fiber cable in which a plurality of multicore fibers like this optical fiber is bundled to form a cable. Generally in the multicore fiber, such a tendency is observed that crosstalk is prone to occur in which optical signals propagated through cores interfere with each other. It is known that this crosstalk depends on the bending radius of a multicore fiber and is reached at the maximum at a predetermined bending radius. Therefore, in Patent Literature 1, in order to decrease crosstalk, a bending structure is additionally provided to a multicore fiber in such a manner that a bending radius Rth given by a predetermined expression takes the smallest value.
[Patent Literature 1] JP-A-2011-197661